1. Field of the Invention
The present invention relates to a composite material which is prepared by connecting a sintered body of cemented carbide or the like to a surface of a substrate of steel or the like, and a method of manufacturing the same. More particularly, it relates to a composite material which can attain stress relaxation and a method of manufacturing the same.
2. Description of the Background Art
As techniques for connecting materials having remarkably different linear expansion coefficients such as a metal and ceramics with each other, the following methods are known in the art:
(1) Japanese Patent Laying-Open No. 52-50906 (1977)
A shock-resistant cemented carbide member having a large Co content is interposed between a cemented carbide cutting member having a small Co content and a medium carbon steel member for connecting these members, and these three members are heated and pressurized to be integrally connected with each other by diffusion of cobalt.
(2) Japanese Patent Laying-Open No. 53-1609 (1978)
Sintering powder having excellent fusibility with respect to a cemented carbide member and a base material of steel or the like is arranged between these members, and these three members are integrally sintered and connected with each other by energization pressing.
(3) Japanese Patent Laying-Open No. 7-3306 (1995)
A cemented carbide member for connection is interposed between a hard cemented carbide member and a steel member. A binder phase ratio in the cemented carbide member for connection is 10 to 45 wt. % greater than that in the hard cemented carbide member.
(4) Japanese Patent Laying-Open No. 6-287076 (1994)
A gradient functional member having a gradient mixed layer consisting of a metal and ceramics arranged between metal and ceramic members is energized and sintered by a forming outer frame and upper and lower push rods. The mixed layer has an inclined composition, i.e., a concentration gradient (composition change) of the components. The energization is effected along a pressure axis direction, i.e., from the first push rod toward the second push rod through the gradient functional member. In this case, the thickness of the forming outer frame serving as one of energization paths is varied to form a temperature gradient which is responsive to the inclined or gradient composition.
While each of the aforementioned techniques (1) to (3) attains its object, stress in the composite material is easily unbalanced in actual manufacturing, due to the difference between and volume ratios of the materials forming the respective layers. Consequently, the composite material is insufficient in durability or the like.
In the technique (4), on the other hand, it is difficult to obtain a gradient functional member of excellent quality due to influences exerted by the conductivity of the upper and lower push rods, the sectional area of the forming outer frame, clearances between the forming outer frame and the upper and lower push rods and the like. Particularly when the connection area is large, the forming outer frame for energization is so extremely increased in size that high power is required and the cost for the outer frame is increased. Further, the shape of the composite material is disadvantageously restricted by that of the forming outer frame, due to sintering/connection through the forming outer frame.
While a cemented carbide member is connected with a steel member by brazing in general, the following problems are known in relation to this technique:
(1) The connection strength is reduced under a high temperature environment, due to softening of the brazing filler metal.
(2) The steel member cannot be heat treated after brazing, for a reason similar to the above.
(3) The brazing is performed in a separate step, and hence the manufacturing cost is increased.